This invention is directed to a method and system determining the pH of a substance. More specifically, it relates to noninvasive optical pH measurement of a substance, where physical contact of the substance is undesirable.
Quality Control (hereinafter “QC”) devices and methods have become an increasingly important part of industry and healthcare over the last few decades. Typically, QC devices utilize invasive methods such as testing with probes, and/or substance withdrawal techniques to assess whether the substance meets its threshold guidelines. However, invasive techniques like the ones employed in many QC apparati are not suitable for applications that require a substance to be part of an entirely closed system, or where substance loss is undesirable.
Specifically as it relates to healthcare, QC has traditionally occurred at the site of the manufacturer, as opposed to the point of use. However, with the development of new contrast agents and other unstable pharmaceutical products, it may be necessary to perform compounding or processing steps immediately prior to administration into the patient. Prior to injection, the safety and efficacy of the substance must be ensured.
In such a QC apparatus, ensuring the safety and efficacy of the pharmaceutical product being tested may occur by acquiring, for instance, the pH, temperature, concentration and/or volume of the agent while comparing those values to proper end-use values prior to administration, all without the substance leaving a closed system. In addition, a QC system that was entirely closed may operate directly at a patient's bedside, potentially obviating the need of a bedside pharmacist.
One particularly important QC parameter may be the measure of the degree of acidity or alkalinity (pH) of the substance. Methods and devices that have been commonly used to measure the pH of solutions include litmus paper tests, pH electrodes, and pH indicator dye. While these methods may be accurate and robust, they are undesirable in situations that require complete sterility, particularly fast response time, or where substance loss is a concern (i.e., closed system bedside QC devices).
For instance, in the context of a bedside QC device, use of a pH dye may be problematic in that the addition of a non-active ingredient to a pharmaceutical product may have harmful implications to the patient. With regards to pH probes in QC devices, similar issues arise. The sterility of the pharmaceutical must be ensured, and the use of a probe heightens the opportunity for the substance to become contaminated. Furthermore, the above-mentioned techniques are not ideal for applications in which the substance being tested is expensive, where even the smallest amount of substance loss significant.
The use of optics to measure physical properties of a substance is well known. For example, absorption spectroscopy has been used to measure the concentration of ions such as calcium blood and ultraviolet/visible absorption spectroscopy is often used to detect the molecular content in liquid samples. However, the use of optics to rapidly determine the pH of a substance that is entirely part of a closed system would be desirable.
Therefore, what is needed is a noninvasive, optically based method and system to determine the pH of a solution, thereby obviating the need for invasive techniques such as pH probes and indicator dyes that may contaminate a substance or pharmaceutical product.